The present invention relates to fiber optic systems and, more particularly, to a gas blocking device used to permit the passage of optical fibers while preventing the passage of gas therethrough.
Repeaters are commonly used in fiber optic systems to amplify optical signals being transmitted over long distances. A repeater body is coupled to a fiber optic cable at each end. The repeater body houses electronic circuitry and lasers used to amplify the optical signals. Lasers and electronics housed in the repeater body should be maintained under very dry conditions, because the slightest amount of condensation in the repeater can cause arcing. Arcing can be devastating to the operation of the system. Maintaining these very dry conditions is most important in undersea applications but also applies as well to terrestrial applications.
To achieve these dry conditions, prior to installation, the repeater housing is vacuum drawn and the air is replaced with pressurized nitrogen to prevent moisture from entering the repeater housing. To enable the repeater housing to maintain the pressurized nitrogen, it is conventional to route optical fibers entering and exiting the repeater through a seal. One known system for creating the seal includes routing the fibers through a plastic tube on the outside of the repeater housing. A compressible rubber stopper is then inserted in one end of the plastic tube to seal the end of the plastic tube. The rubber stopper is punctured one hole at a time for each optical fiber in the bundle and each fiber is routed through a respective hole during the puncturing process. The compressible nature of the rubber stopper is intended to create an individual seal with each optical fiber. At least one drawback of this conventional seal and sealing method is that the assembly is labor intensive.
Additionally, this type of sealing assembly is better suited for water blockage. Because the sealing assembly relies on a friction fit between the rubber stopper and the plastic tube and fibers, the nitrogen in the pressurized housing interior could still potentially escape through the seal if tight tolerances are not achieved. Furthermore, this existing sealing assembly had difficulty accepting more than eight fibers due to the inherent material properties of the rubber stopper and the difficulty in drawing the fiber through the rubber. This sealing assembly thus could not easily accommodate the increased number of fibers in high fiber count cables.
Accordingly, there is a need for a gas blocking device that is easier to install, that has improved sealing properties, and that is capable of accommodating an increased number of fibers.
In accordance with the present invention, an optical fiber device is provided. The optical fiber device comprises a housing that is vacuum drawn and pressurized with a gas to prevent moisture from entering the housing. An optical fiber holding tube extends through a wall in the housing such that a first end of the optical fiber holding tube is contained in the housing and a second end of the tube is located outside the housing. A plurality of optical fibers extends from the first end of the optical fiber holding tube to the second end of the optical fiber holding tube without interruption. A gas blocking device is attached to the first end of the optical fiber holding tube. The optical fibers extend through the gas blocking device and are surrounded by a material, creating a seal that prevents the gas from passing through the optical fiber holding tube.
In accordance with another aspect of the present invention, a gas blocking device is provided for use with an optical fiber holding tube. The gas blocking device comprises a fiber containing body having a passageway for receiving a plurality of fibers from the optical fiber holding tube. A material, such as hot melt glue, at least partially fills the passageway of the fiber containing body and surrounds the plurality of fibers passing through the passageway. A fiber organizing insert is secured at one end of the fiber containing body and has a plurality of fiber receiving holes for receiving respective ones of the plurality of fibers. The fiber organizing insert and the fiber containing body preferably include cooperating key structures such that the fiber organizing insert is prevented from rotating with respect to the fiber containing body. A locking member preferably secures the fiber organizing insert to the one end of the fiber containing body.
In one embodiment, the passageway within the fiber containing body includes a wide portion, a narrow portion, and a tapered portion between the narrow portion and the wide portion. The narrow portion of the passageway preferably has an inside diameter dimensioned such that the fibers act as strength members within the material in the narrow portion. For example, the ratio of the cross-sectional area of the fibers to the cross-sectional area of the narrow portion is about xc2xd. The fiber organizing insert is secured within the wide portion of the passageway and is preferably made of a substantially non-compressible material.
In accordance with a further aspect of the present invention, the gas blocking device is provided as an assembly comprising the fiber containing body for receiving the fibers and the material, the fiber organizing insert adapted to be positioned at one end of the fiber containing body, and the locking member adapted to lock the fiber organizing insert to the fiber containing body.